Kava is a tropical evergreen shrub with heart-shaped leaves and woody stems. Its scientific name is Piper methysticum.

Pacific cultures traditionally use the kava drink during rituals and social gatherings. To make it, people first grind its roots into a paste.

This grinding was traditionally performed by chewing the roots and spitting them out, but now it’s typically done by hand ().

The paste is then mixed with water, strained and consumed.

Its active ingredients are called kavalactones, which account for 3–20% of the dry weight of the root of the plant ().

Studies suggest kavalactones may have the following effects on the body:

Reduce anxiety ()

Protect neurons from damage ()

Reduce pain sensations ()

Reduce the risk of cancer, though the evidence is limited to mice (, , , )

Most of the research to date has focused on kava’s potential to reduce anxiety.

It is largely unknown how kavalactones produce these effects, but they appear to work by affecting neurotransmitters in the brain. Neurotransmitters are chemicals that nerves release to communicate with each other.

One of these neurotransmitters is gamma-aminobutyric acid (GABA), which decreases the activity of nerves (, ).

Summary The roots of the kava plant contain compounds called kavalactones. These compounds are responsible for many of kava’s beneficial effects.

Dosage

Kava supplements may list kavalactones in milligrams or as a percentage. If the content is listed as a percentage, you will need to calculate the amount of kavalactones it contains.

For example, if one capsule contains 100 mg of kava root extract and is standardized to contain 30% kavalactones, it will contain 30 mg of kavalactones (100 mg x 0.30 = 30 mg).

To reach an effective dose within the range of 70–250 mg of kavalactones, you would need to take at least three capsules of this particular supplement.

Most extracts of kava root contain 30–70% kavalactones ().

Summary Kava is available in many forms. Avoid products with “proprietary blends.” Instead, look for products that tell you the kavalactone content per dose, or the percentage of kavalactones the product is standardized to contain.

While kava may be beneficial for anxiety, many people are concerned about its potential side effects.

In the early 2000s, several cases of liver toxicity were reported related to kava consumption ().

The US Food and Drug Administration later warned about the risk of liver damage associated with products containing kava ().

Its use has even been banned or restricted in many countries, including Germany, Switzerland, France, Canada and the UK.

However, the ban in Germany was later lifted due to poor evidence of related risks ().

Kava is thought to harm the liver in many ways, one of which involves how it interacts with certain drugs.

The liver enzymes that break down kava also break down other drugs. Thus, kava can tie up these enzymes and prevent them from breaking down other drugs, causing them to build up and harm the liver ().

Adulteration is another reason kava products are thought to be unsafe (, ).

To save money, some companies use other parts of the kava plant, such as the leaves or stems, instead of the roots. The leaves and stems are known to harm the liver (, ).

Still, several analyses of studies on the topic have found no evidence of liver damage in people who have taken these supplements in the short term, or about 1–24 weeks (, ).

Therefore, people without liver injuries and those who are not taking medications that affect the liver may be able to use kava safely in appropriate doses for about one to two months ().

Summary Though kava can be used safely in the short term, it has been linked to liver problems. It’s best to consult a doctor before you start taking kava, since it may interact with certain drugs. Certain products may also be adulterated with other parts of the plant.